All experimental treatments were carried out in two temperature controlled
rooms on 12-hour light:12-hour dark cycle. The unit, designed
to regulate the environmental temperature at 22±2 °C, was
insulated and fitted with thermostatically controlled heaters. The second
unit, in which temperatures could be varied between 5 and 45±2 °C,was
insulated and fitted with both heating and refrigeration units. All units
were constructed without outside windows. The heaters (20 kW) were
attached to a duct system (10×15 cm), and vented through three of the
four walls midway between the floor and ceiling of each isolation
chamber. External air was drawn over the heaters and vented through
holes in the bottom of the duct system. This provided for a uniform
distribution of heat within each chamber. A large refrigeration unit was
installed into the fourth wall of the isolation chamber at variable
temperatures (i.e. 22 °C and 40 °C, on a 12-hour cycle). To permit rapid
cooling to the desired 22 °C temperature cold air was re-circulated after
the 40 °C heating period. The detailed description of these rooms has
been given by Taylor (1968 a). Body temperature measurements were
made twice daily (at 0900 h and 2100 h)when the animals were exposed
to intermittent heat load (12 h at 40 °C) and dehydrated. The animals
were randomly allocated to the various experimental treatments